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A collection and selection of data has been carried on the Merino Beira Baixa ewes at Escola Superior Agraria (Agricultural School) in Castelo Branco (ESACB) in Portugal from 1981 to 1989. According to the birth type of females (single or double) their average age at the time of first lambing amounted to 599.85±150.47 days and to 574.13±147.06 days. Diferences were not significant. However this parameter was influenced by the “year” factor (P<0.01) Is was shown that lambing interval (IP) did not depended on parturition months inside the season but depended on parturition months between the parturition season (from january to april 322.66±79.31 days and from august to december 380.67±73.81 days). The IP revealed significant diferences (P<0.01) in terms of ewe age at lambing. The apparent fertility rate, ptolificacy rate and numerical productivity are, in 1981-87 and 1987-88, 86,6% vs 85,9%, 114, 2% vs 112,3%, 92,7% vs 84,9% respectively. All these rates were influenced by the ewes age at lambing. Reproductive parameters in period with altered reproductive management (two autonomous herds without ewes transference) are diferentes, favourable to Autumn mating season. Analysis was carried on further reproductive parameters.

The region of Castelo Branco is the 4th main region of Portugal in number of ewes. Sheep production is the major importante activity of its farming systems. Beira Baixa Merino is the most common breed of the region and it is used as a triple purpose: milk, meat and wool. Nowadays, milk has becoming the most importante production. The new production conditions, with acession to the Common Market, lead the farmes to change some components of farming systems. To study how this changes must occur, an inquiry was made to the farmers, that allow a characterization of production systems, as the basis of future work. This paper results from the inquiry referred, and it’s an approach to the production systems of Beira Baixa Merino. Some constraints to the developpment are pointed.

A collection of data has been carried on the Merino Beira Baixa sheep at the Escola Superior Agrária (Agriculture School)in Castelo Branco (ESACB)in Portugal from 1981 to 1987. According to the birth type of females (single of double), their average age at the time of first lambing amounted to 600,10 ± 158,86 days and to 583,90 ± 159,78 days.Differences were not significant. However this parameter was influenced by the "year" factor (P<0,01). It was shown that the intervals between lambings (I.P.) did not depend on the parturition months inside the seasons, but depended on parturition months between the two parturition seasons (from January to March 296,4 ± 64,22 days and from September to November 380,0 ± 71,5 days). The "I.P." revealed significant differences (P<0,01) in terms of the conception age. The average apparent fertility rate amounted to 86,6%, the prolificacy to 114,2% and the average numerical productivity to 92,7%. All these rates were influenced by the ewes age at lambing. Analysis were carried on further reproductive parameters.